Decoding 10 Gigabit Ethernet Transceivers

With components fulfilling the same basic function available in five different form-factors, at first look the world of 10Gbps optical transceiver modules looks a bit cloudy. However, with the demand for more compact space, the 10G form factors have been developed along the way from the earliest XENPAK to modern SFP+. Since then, the 10 Gigabit Ethernet transceivers are gaining more and more popularity on the market.

10Gbps transceivers are also known as 10GbE or 10GBase transceivers. These transceivers transmit data at a base rate of 10 Gigabits per second typically using Ethernet protocol. A variety of optical component and systems vendors began working on 10Gbps standards (called Multiple-Source Agreements or MSAs) in about 2000. The following is a list of the MSAs published over the subsequent years:

XENPAK, published in the year of 2001, was by far the largest in physical size. Driven by large systems vendors, this XENPAK standard was intended to support essentially any optical application a system vendor may want to deploy. At that time, 10Gbps optical interfaces supporting transmission distances of 80 km or more were of a size and heat dissipation that required a relatively large (by today’s standards) package size.

When recognizing the size of the XENPAK is too limited, vendors in this field began working on alternative standards. Over the following two years, three alternative MSAs, namely XPAK, X2 and XFP were published. When these standards were written they were intended to enable optical interfaces supporting up to about 10 km. While the XPAK standard was not a commercial success, the X2 and XFP form-factors both saw considerable deployment. As optical technology has advanced over the last ten years, X2 and XFP modules have been developed to support all of the high-power, long-distance applications once reserved to the larger XENPAK transceivers. The following is a comparison of the 10G transceiver sizes.

Five years after the first 10Gbps optical transceiver standard was issued, a new MSA was published called the “SFP+”. This agreement has been the basis for the most commercially successful 10Gbps optical transceivers by a large margin. There are several reasons for the success of the SFP+ standard:

• Flexibility – The SFP+ standard builds on a previous one, the SFP MSA (primarily a 1Gbps standard). SFP+ modules are the same physical size as SFPs and the SFP+ standard allows for either type of module to operate in the new SFP+ slots.
• Small Size – As shown in the above figure, SFP+ modules are one tenth the size of the original XENPAK 10G modules and are the same size as the popular fiber SFP modules. This small size allows the design of systems with 10G ports of the same density as previous generations with 1G ports.
• Low Cost – Since SFP+ modules share many components (bezel, housing, latch/locking mechanism) on the previous SFP standard, the cost of the new 10G modules inherits the low cost of these components. SFP+ units are also lower power, contributing to cost savings.

Systems (such as routers, switches, media converters) designed within the last two or three years have implemented, with very few exceptions, the SFP+ standard for 10Gbps ports. If used – or new equipment of older design – is being considered, users must be careful to identify what type of port is built into their gear. So remember to refer to the equipment manufacturers specifications when choosing the suited 10GBase form-factor.

When considering new or used equipment for a new network build or expansion, attention should definitely be given to the type of 10Gbase ports in that equipment. One important reason is capital costs. Older gear offering XFP, X2 or XENPAK ports may be attractive due to what seems like very low prices. However, the cost of equivalent 10GBase optics in those older form factors is 2X to 3X the price of SFP+ based modules. Therefore, when the cost of the optics are included, total system costs may be higher. Other costs to consider are:

• Power – The older XFP, X2 and especially XENPAK gear, both the host system and the 10GBASE optical modules, consume more power than the SFP/SFP+ modules (like 10GBASE SR SFP module). Power costs include capital outlays for larger power/battery plant as well as operational cost of the electrical power itself.
• Rack Space – Depending on the location, space in equipment racks can be quite expensive. Equipment utilizing the older 10Gbase interfaces is almost always substantially less dense, consuming more rack space per 10G interface available.

Through the above analysis, we can see that SFP+ is clearly the winner! With its substantial advantages in cost, size and power, along with flexibility to support any type of optical interface while maintaining backward compatibility with previous SFPs, the SFP+ is the clear winner in the 10GBase optical transceiver market. Although newer standards for higher speed, like 40Gbps and 100Gbps have already been launched, it can still be predicted that, SFP+ based optical transceivers are bound to continue to dominate the market for 10Gbps modules for the next 10 years or more.

Originally published at https://www.linkedin.com/pulse/decoding-10-gigabit-ethernet-transceivers-kelly-zeng